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C. W. STONE AND H. M. HOBART. ELECTRICLTY ITRANSFORMING AND CONVERTING APPARATUS.

APPLiCATION FILED SEPT-6, 1916- 1,337, 1 O0. Patented Apr. 13, 1920.

8 SHEETS-SHEET 1.

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Inventor-s: Char-'|esW.StOhe, Herr-I \"l'LHobar-"c,-

b9 ,fiw/r M c. w. STONE AND H. M. HOBART.

ELECTRICIIY TRANSFORMING AND CONVERTING APPARATUS.

APPLICATION FILED SEPT.6, 1916- 1,337,100. P ed Apr. 13, 1920.

8 SHEETS-SHEET 2.

Inventor-s: Char-lea W Stone, H enr- Id TTIHQba Ft, b yfw Z Their" fittor'neg.

c. w. STONE AND H. M. HOBART.

ELECTRICITY TRANSFORMING AND CONVERTING APPARATUS.

APPLICATION FILED sEPT.6,191a.

1 ,33'7, 1 0O. Patented Apr. 13', 1920.

8SHEETSSHEET 3.

Inventor's:

Charles \NStone,

Harv-'9 l'fiHobart, b hm. M

Theirafittorrwes.

C. W. STONE AND H. M HOBART.

ELECTRICITY TRANSFOHMING AND CONVERTING APPARATUS.

APPLICATION FILED SEPT=6, I916.

Patented Apr. 13, 1920.

8 SHEETSSHEET 4.

Fig.

Inventor-s: Charles W.St.one, Her-1 9 TT'LHobart,

Their-'fittor-nes.

C. W. STONE AND H. M. HUBART.

ELECTRICITY TRANSFOHMING AND CONVERTING APPARATUS.

APPLlCATION FILED sEPT.6.1916.

,337 I Patented Apr. 13, 1920.

8 $HEET$SHEET 5.

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Inventor-s: Char-'les W. Stone. He P5 mHobart,

Their'aqttOr'heg.

C. W. STONE AND H. M. HOBART. I ELECTRICITY TRANSFORMING AND CONVERTING APPARATUS.

APPLICATION FILED SEPT-6, 1916.

1,337, 100, Patented Apr. 13,, 1920.

8 SHEETS-SHEET 6.

' A (5 FT2J8. pimwimwmiwwm sq I3 wmwmw? MILAN/I ATLANTA MIQ INIA AN I/ IA C IWkTiBS.W. Stone,

l-lenrym Hob awn,

7 segment C. W. STONE AND H. M. HOBART.

ELECTRICITY TRANSFORMING AND CONVERTING APPARATUS.

' APPLICATION FILED sums. 1916.

1,337,100. Patented Apr. 13, 1920.

8 SHEETS-SHEET 7.

One -furth q the fi'an' end connect/ans q: a 20 ml: Synchronous Converter- 25 w/th 24 commutator segments per-po/e. '2'

A everb :ommu'batcr nch ran aux Con vortar.

Separdar- Wmdmg Pr/rnary I I Slots for- Secondary W/hd/hg UU'I] U HUI] Inventors: Charles W. Stone Hem- M.I-lobar"t Their Attorney.

C, W. STONE AND H. M. HOBART.

ELECTRICITY TRANSFORMING AND CONVERTING APPARATUS.

APPLICATION FILED SEPT.6, 1916.

1,337, 100. Patented Apr. 13, 1920.

8 SHEETSSHEET 8.

Cammutator Synchronous Converter MM/n9 Fig.25.

Secondary W'nd/n9 0f 7F'ansformer IHH 9 03m 0 mm b Q w u x m o H IIIIH Pr/mary W/hdiflg of 7Fansfor-mer -QQQQQQQQQQQQQQQ--- QQQQ.O.O.O.:.QOOOQ-QOOQOQO iiiiii H226 Wind/n9 Inventors: SW5 1%,- Charles W. Stone, Pmh r Henry M.|"|ObaTt,

b5 M; M Then" Attorney,

" STATES PATENT cnmns'w. STONE AND Emmy. in. HOBART, or scnENEc'rADY, imw Yonx;

nssrenons a'o en vnm nnncrmc COMPANY, "A conr'omrron 01" NEW r m'iisronmme AND commune 'ArrAcaArusi f Specifications Letters IEatentl. i :PafiQntdrApr 13,-192D;.

f A pplinatiortflled-September-G, 1916; serial mr. 118;635.

United States, "residingat; Schenectady,

county of"-Schenectady,-- and State of New-- York, have invented certain new and useful Improvements Electricity Transforming end Converting Apparatus, of "which the following isa specification.

lates to Y electricity transntion Our in.

forming-"and convertimr apparatus,- that is: to say, tot ap'paratus" or -performing-=thedouble functionioftransforming alternating current electricity "from *one voltage to: anotfii ana oi cp ivcltingoneform of: electric F energy' toener'gy'ofad fferent; characteristic.

More spe'cificallfl "our; invention relates to '-"-"electr1cal machinesifor receiving: high pressure polyphasealternating current electri'city from asupply systcm and delivering relatively 'low 'pressure direct current electricity'toa distribution system.

Thetransformation' and 1 conversion of high pressure alternati'ngcurrent electricity to low pressure direct current electricity is nowfausually"-a ccomplished by i stationary step-down transformers and synchronous J converters; "The stationaryv transformers step down the high pressure electricity to voltages suitable for the synchronous converters, and th'e'jlatter machines receive the low pressure alternatingcurrent electricity:

throughsuitable slip rings and deliver corconsequence, the alternatingcurrentvoltage respondingly lOW pressure direct current electricity at suitable commutator brushes.

It is'a wellknown fact that'the alternating cill'rer'itvoltage impressed upon the alternating current side of a synchronous converter bears a direct relation to' the' direct current voltage" The direct current voltage is determinediby the character of the load with which the 'machine is to be used, and, in

of the converter is almost invariably different than the; voltage ofthe supply circuit, which necessitatesthe installation of some formpf transforming device between the supply circuit and the converter; Accordingly, as above stated, ithas been the common practice in the'past to 'use transformers. [n city'fsub-station's almost universally airblast typetransrormers have-been used. In rural stations both air-blast and oil and oil S'roNE- and HENRY M. HOBART, citizens of theused;

electricalconnections from the transformers to 1 the synchronous converters-are.also-costly: and liableto'cause trouble 'Some of' theseobjectlonsto the: useof transformersi have forced operating: companies; to use-motor. generatorsets; windingthe stator-of: the 3x1:-

ternating currentr' machine for Ithe line/1P0 tential. 2 Motorgenerator sets areztlnore... costlyand-zfar less efiicient than'synchronousr converters'vwith transformers, hence a natural 'resultfor engmeersto endeavor .to ach eve has been-to devise :a machine which wassome compromise between the synchronous converter and motor generator set: This endeavor has resulted inthe develo ment of the motor converter, .which'we Wlll not attempt to discuss herein, except to point out that the motor converter is-a compromise on .the higher frequencies asit is somewhat less expensive than .a. motor-gen erator set and somewhat'more efiicient, but is less efficient and more costly than avsynchronous converter for the same'whrk.

The principal object of our present invention'is to provide an ,improvedzelectricity:

transforming and v converting' apparatus. In this connection our inventionl aims broadly to provide a novel and improved form of apparatus for performing the double functionsof transforming alternating current electricity from one voltage to another and of converting alternating current energy into. energy of different'characteristics. The particular object of our-present invention isto provide an improved ap- I invention, we provide an electricity transforming-and converting apparatus compnsing essentially a rotatable transformer in combination with suitable electricity eonverting-means of-therotary type, such as a sure direct current electricity, and vice versa, the electricity. converting means is preferably of: thev synchronous converter type having anarmature winding rotatably mounted within the influence of a stationary X magnetic field system. The transformer is then mounted on the same shaft as the armature: core ofthe synchronous converter, and the transformer and armature windings thus rotate u as a single; mechanical unit. The

niagnetic'cores .of the armature and trans former windings may be independent and arranged side by side on-the rotatable shaft, or these two cores maybe combined into a single .core, as for example by slotting the interior of the armature core for the accommodation of the transformer windings. The primary winding of the transformer is electrically connected to suitable electric current collecting means, such for example "as-slip rin s carried on the rotatable shaft. 3 The secon' ary winding of the transformer is electrically connected to the armature winding of the dynamo-electric machine, and-one of'the particular advantages of our present arrangement is that the secondary winding can be tapped into the armature winding of the converter at a greater number-of places per. pair of poles of the latter than is-practicable in the case of any existing apparatus. with which we are familiar.

--Br-iefiy, Fthe principal advantages of our improved apparatus are that'all of the high efficiency and. low cost of the synchronous converter are retained, all of the high efii'ciency of the transformer is retained, and the transformer can be wound for the ordinary line potentials commonly used, without the necessity of the installation of separate transformers and the leads thereto, thus making our apparatus a self-contained unit of high efiiciency, low cost and excellent operating characteristics. In our improved apparatus, the synchronous converter becomes a better operating machme, besides being of lower cost, due to the multiplicity of phases, whereby the hot spots in the armature winding of the synchronous converter are substantially eliminated. The

transformer, due to the fact that it is rotated, can be more efficiently cooled than any form of stationary transformer, thus Where the apmaking it possible tobuild a jtransformer occupying considerably less space than heretofore. These and other advantages of our improved apparatus will -be brought-ou'tand discussed in greater detail hereinafter.-

The novel features of the invention which we believe to be patentably characteristic thereof are definitely set'forth in the appended claims. The invention itself and the construction and mode of operation of ap: paratus embodying the invention will be better understood from the following descriptions and discussions taken inconjuno-i;

tion with the accompanying drawings ,in which:

. v, 51 Figure l is a diagrammat c-elevatmn of an electricity transforming and converting. 1 apparatus embodying our present invention;

Fig. 2 is;a diagramof-the electrical-connec; tions .of .the apparatus a of Fig.1; Eigsg 3;

and 4 are diagrams of modified connections of certain of the windings ofthe apparatus;

Figs. 5, 6,7 and 8 are detail.views,,sh0-Wing. a practical construction; of the transformer.

9 to 19, inclusive, are diagrammatic Views .of

employedin our improvedpapparatus; Figs.

various arrangements we; have found particula rly advantageous for obtainingamultlplication of phases in our improvedlap f paratus; Fig. 20 is a diagrammatic viewof a transformer designed to produce a multiplication of phases particularly adapted for use-in our improvedapparatus; F 21 and 22 are diagrams of the electrical,

connections of the primary and secondary windings, respectively, of the transformer of Fig. 20,1 igs. 23 and-25 are-practical winding diagrams ofphase-multiplying transformers embodying the broad principle of phase-multiplication of the transformer of Fig. 20; and Figs. 24c'and 26 are .detail views of the slotted laminations of the magnetic cores of the transformers represented in Figs. 23 and 25, respectively.

The general construction and'principle of operation of the machine of our present invention will be most readily comprehended by reference to Figs. 1 and-2 of'the accornpanying drawings. The machine-is mounted on a suitable base 30; Bearing posts or; pil-g lar blocks 31 are suitably secured to the base and provide the bearings for the rotatable. shaft 32 of the machine. It will be'observed that the shaft 32 hason'ly two bearings,'one at each. end. The shaft 32 carries a stepdown transformer T andithe rotorof a dynamo-electric machine B. High tension alternating current electricity is fed from the three-phase supply mains 33 to the primary winding 34 of the transformer T- by means of slip rings 35: and cooperating.

brushes 36. The slip rings35 are so-proportioned as to carry the high pressure'current' absorbed by the machine at its rated load; Machines of the character for which our invention is particularly designed are n0w'usu ally required foroperation from circuits with pressures between 5,000 and 12,000 volts, and, since at these pressures the current for agiven power is very much smaller than for pressures of 150 to 600 volts, such as heretofore employed for the slip rings of a synchronous,- converter= fed by :stationary transformers, the amount of space and the weight andcost of material devoted-to the slip rings; is relatively very .small.- .The brushes by means :of which the current is conducted'to-the slip rings-35 are omitted in Fig. 1,: but are diagrammatically indicated in Fig. 2,'and therigging by which the brushes are carried has been omitted in both figures in ordertosimplify the drawings. It will of course be understood that the brushes and brushrrigging may be of' any accepted-design suitable for machines of this generalxtypepw- H. The. sli rings 35 are electricallyiconnected to t e terminals of the primary winding-'34; of theitransformer T. -While we have illustrated a single transformer '1, it is tobe understood that two or more .transformers may be mounted *on' the shaftv 32 if desired.

.The preferred construction of the transformer or transformers T- will be described in detail hereinafter. In the embodiment of our invention illustrated in Fig. 2 the primary winding 34 consists in effect of two three-phase wlndings one of which is deltaconnected and the other star-connected, and the .two three-phase primary windings are preferably connected together and to the slip rings as indicated. In the arrangement of Fig. 2 it will be noted that the delta-connected threerphase transformer constitutes in effect-the neutral of the star-connected three-phasetransformer. The star-connected three-phase transformer may have its terminals connected to the terminals of the deltaconnected three-phase transformer, as diagrammaticallyrepresented in Fig. 3 of the drawings. and in some cases this arrangement will be preferable to that represented in Fig. 2.

The secondary winding 37 of the transform er T has two separate coils for each coil of the primary winding. The secondary winding thus has twelve coils which may be arranged to form a closed ring or mesh wind ing, as diagrammatically represented 1n Fig. 2. If desired the twelve secondary coils may be connected to form a twelvephase star, as diagrammatically represented in Fig. 4:. Whether mesh or star-connected the twelve terminals of the secondary winding are similarly connected to appropriate points of the armature or rotor winding 38 of the dynamo-electric machine R. The machine R is in substance a synchronous converter, andthe armature winding 38 is thus similar to the armature winding of the are also connected to the brushes 41,- as will,

be well understood by those skilled inthe art. The field winding 40 has such anumber of poles asto produce the desired speedof rotation of the rotor of ourjimproved-maa chine, as will also be clearly understoodby,

those skilled in the art.

Before proceeding further with the de:

tailed description of the constructionof the improved machine of our present invention,

it is desirable at this point to .contrast the general arrangement illustrated in Figs, 1 and 2 with the arrangement heretofore, and now, usual in the art, which consists of a synchronous converter, ,such as that whose armature, commutator and field fare represented at 38, 39, and 40, respectively, of Figs. 1 and 2, but which is, in addition,- provided with a member of large sliprings connected into appropriate parts of the armature winding. Through brushes bearing Euponthese slip rings, current is supplied'to the synchronous converter from stationary transformers. In such an outfit, the voltage at the slip rings must bear a definite relation to the desired commutator voltage. Since the latter is usually of the order of 220 to 7 00v volts, the pressure at the collector rings, must also be of similar .low values. In such sets as are used by the large electricity supply companies in cities, the current which has to enter this synchronous converter at each ring often runs into many thousands of ampheres. Six slip rings are usually employed, and when each has to carry several thousand ampheres it is obvious that the space occupied by and the weight and cost of the slip rlngs may run to formidable proportions. I

When the space occupied on the-shaft by such low pressure slip rings is replaced by a step-down transformer and threehighpressure slip rings, as illustrated in Fig. 1 of the accompanying drawings, although the shaft has to be of slightly largerdiameter to carry the increased weight of the trans.

former, the length of the shaft between bearings is but little greater than in the usual synchronous converter supplied by stationary transformers. Furthermore, the space in the sub-station occupied by the stepdown transformers in the heretofore, and now usual, arrangement is saved in our improved outfit, and when such sub-stations are located in cities where land is expensive this saving of floor space is of much importance. -l-Ieretofore, the stationary transformers have usually been of the type in which theactive materia'l', comprising iron, copper, and insulation, is immersed in large tanks of oil, inwhicharealso immersed coils through which water is circulated to maintain: the oil cool and to thus dissipate the losses inthe transformer. Inlarge cities the outlay forthe Water required for such cooling purposesis an item which represents an appreciable-proportion of the total costs of operationof a sub-station. As an alternative, I transformers aresometimes employed of a type which-are kept 0001 by the forced cireulation through them off airysupplied by a blower which is in turn driven by a motor. In the-improved: maohineof-our present invention. the transformer is mounted on a rotating shaft-,and m) transformer plant-of either of the-types just described is required;

Ithas already been mentioned that the synchronous mnv'erter now usual the art is customarily provided with six slip rings. Formerly, onl y three sliprings wereemployed,;and thisleads us toa consideration o f-a very important property of synchro nous converters; namely,-that they are insevera'l'respects improved the greater number of taps through which the alternating current electricityis sent'into the armature winding; When onl y-three slip rings are provided, there-cam be but three taps-per pair'of poles. With the present usual practice of'providing six slip rings, there are six taps per pair of' poles. It has been proposed that twelve slip rings should be provided. This would permit of: twelve tapsper pair of poles, but no such departure has been made incommercial machines, it having been-considered that. the multiplicity of slip rings, each with its brushes-and brush-rig ging, would introduce-complications not justified by the -improvement which would thereby be effected inthe synchronous converter. However this may be; it'will be observed that by mounting, the step-downtransformer on the rotating shaft of a synchronous converter, it becomes practicable to supply: alternating current 1 electricity to the armature of the converter through a large number of taps: per pair of polesand without encountering any of the embarrassments mentioned; since the-=lowpressure electricity is not carried to the synchronous converter through slip rings. The advantages of employing large numbers of taps in the armature winding of the synchronous converter per pair of poles will be more particularly mentioned hereinafter.

The mechanical and electrical design of the step-down transformer'T carried on the rotatable shaft 32 will be understood by reference to Figs. 5, 6, 7 and 8 of the accompanying drawings: The magnetic core of: the transformer consists of twomain sections 43 and: 44; The core-section 43 is made upiinthe usualm-anner of= star shaped sesame:

punchings of laminated magnetic material, and when the primary and: secondary windiugs have been properly assembled on the six legs or spokes: of this section, the other core-section 44, which is madeup of an'-- nular laminations, is forced: overtheouter circular periphery of the six legs of the star-shaped section.v The two' sections of themagnetic. core aresecurely held together by insulated splines 45. The laminations of the coreesection 43: are heldl togiether by" twodsets'of insulated bolts 46 and 4'3, the latter setof bolts extending through. annular: end plates 48 ateachi end-l of thissection'. of the: magnetic core. The coreisectioni. 44 held together by a set; of insulated bollsa49fi' which extendthronglr the. radial fiangesiefi two hollow cylindrical enidi piates'i 50. and)? 51.. The: end. plates 50 and 5.1 form. housings at each end of the. magnetic 'corefor' the transformer windings and connectionsg. as will: be seen by referenceitoa Fig; 6', and as will bemore fully described hereinafter; The insulation of the! splinesr45- and' of the:

bo'ltsr46, 47 and 49" consists of:v a surrounds ing layer or sheath of insulating material; asv will' be clearly seen by: reference to; Figs: 6' and 8 of the'drawings.

One coil of the primary winding and twocoils. of the. secondary winding are wound on each leg of the star-shaped'coresection 43. As previously mentioned, these coils are assembled before the annular coresection 44 is added. The two coils of the secondary winding 371 are first assembled on the legs of the core-section 43 and the;

four terminals of these coils are suitably-v connectedjto the terminals of" the other coils and to twelveterminal' rings 52, in accordance with the desired scheme of connection, as for example diagrammatically represented in Fig.2 or in- Fig. 4 of the-rdrawings. The terminal rings. 52 are: flat rings arranged in two concentrically disposed groups of sixeach. 'Each terminal ring'is' carefully insulated from the adjacent-mug, as clearlyshown in Fig; 6 of the' dirawings. The terminal rings 52 are connected 1:01 the appropriate points of the armature winding 38 by means of radially disposed conductor strips 53, secured to the rings, and horizontally disposed conductor strips 54 ('Fig. 1')- connecting the outer ends of the strips 53 to the armature winding. It will be understood by those skilled in the artthat there will be twelve conductor strips 53-434 per pair ofpoles of the dynamoelectric machine R, and inFigs. 1, 5, and 6 of the drawings the transformer" connections illustrated are designed for a sin-pole machine R. In Fig. 20f the drawings, thedynamo-electric machine R is diagrammatically represented as a two-pole machine but it will be understood by those skilled in the art that when the machine has a greater number of poles, each pair of poles of the armature winding will in effect be similarly connected in parallel to the terminals of the secondary winding 37 of the transformer T.

The coils of the primary winding 34 are assembled over the coils of the secondarv 'winding37, as shown in Figs. 6, '7, and 8. of

the drawings. The primary coils may be of a more or less triangular cro'sssection in order to utilize to advantage the openings in the magnetic core of the transformer. Thejthree slip rings 35' are carr1ed on' the.outer periphery of the cylindrical'end plate51 and are insulated from each otheryand from the endplate, asclearly illustrated in Fig.6. Conductors 55 suitably connect the coils of the prima vwinding 34 to the slip rings 35 and to eac other. in accordance with the desired scheme of connection, as for example as diagrammatically represented Fig. 2 or Fig. 3.

It is now in order to call attention in greater detail than heretoforeto the nature of the advantages'obtained by employing large numbers ofjtaps per'pair of poles. In the following table the total armature 1 R. lossina'fsy'nchronous converter with six' taps 'p'er pair of poles is taken as 1.00, and there 'are shown'ilrthe table for twelve and twenty-four taps per pair of poles, the relative PR losses in thearniature windings for five different. power factors 2'- Numberoftaps' W second 7 Relative total IR loss in armature winding, that or 3 ina machine with six taps per pair of poles form" being taken as 1.00. the armature winding of a synchronous V converter er a pair of po es. PI=1.00. Pi=0.99. Pf=0.94. P1=0.85. Pf=0.75.

.' l 1.00 1.00 1.00 1.00 1.00 I 0.76 0.77 0.82 0.85 0.88 I 0.70 0.71 0.76 0.80 0.84

It will be seen that the gain is greatest at unity power factor, but that it is still very notable even -at so low a power factor as 0.75. As a matter of fact,- the best practice in the service operation of substations is to maintain the field excitation at such a value that the electricity shall be supplied to the syn chronous converter at practically unity power factor. From an examination of the. above table, it will be noticed that, while the total 1 R loss in the armature winding is twenty-four per cent. less with twelve taps per pair of poles than with six taps per pair of poles, there is a further gain of only six per cent. in going to twenty-four'taps per pair of poles. V In this particular respect of the reduction in the total PR loss, the greater part of theimprovement obtainable by the employment of a greater number of taps per pair of poles is achieved by the use of twelve taps, and it would hardly be Certain conductors, spaced at. equal intervals all around the armature, are subjected to much greater heating than those midway I between them. The magnitude of this nequality is shown in the following table, in the right hand side-of which are given for several power factors, the ratio ofthe loss per gramof copper at the hottest spots in;the armature conductors to the average loss per gram of copper. llhese v figures are given for synchronous converters employing respectively 3,4,6, Hand-'24: taps per pair of poles. 1 g

Numberottapls I v p 2236:33 2 Ratio of loss p'ergram of copper at hottest former into spots in the armature conductors, to average I the armature loss per gram of copper. .winding of the synchronous convert or per pair of poles. Pf=1.00. Pf==0. 99. Pf==0.94. Pf=0.8 5. Pf-0.75.

As already pointed out, it is the conditions at, or near, unity power factor which are usually of chief importance in the service operation of synchronous converters. Directing our attention to the column for unity power factor, it will be seen that while with three taps per pair of poles, the loss in the hottest spots in the armature conductors is over twice as high per gram of copper as is the averageloss per gram of copper; when we come to six taps, the ratio isonly 1.6; for twelve taps, the ratio is 1.2, and for twenty-four taps,-it is only 1.05. In other words, if we employtwentyfour taps per pair of poles, we obtain a close approach to a uniform distribution of heat throughout the armature winding, the greatest variation in the watts 'per gram of copper only amounting to 5 per cent. above and below the average value. When we realize that this fine result, so far as regards the distribution of heat, is associated, as shown by the table firstgiven, with 30 per cent. less total PR loss in the armaprovided, of course, that this can he accomplished by simple and inexpensive means.

In the .followin table are given data which further eznp asize the importance of these considerations.

Npmberottapls rom secon m Relative hottestrspot .loss in armature config 1 du'ctors,.that in a machine with 6 taps per pair "tbe'armamre. ntpolos belng:ta2kenas7100.'

.windinz .ot, the memo- I :mconwartpatrol y 1 If- 1.00." Pf-0.99. Pi-084. Tt=O.85. P!=0.75.

In the hand side of this table are given for various power factors, values for the rela'tive hottest-spot loss in 'the armature conductors, that in a machine with 6 taps er pair of poles being taken as 100. It wifl be 'seen from this table that for unity 'power factor, the use of twenty-four taps per pair of poles is associated with less lthan a'lf as great 'a hottest-spot loss as occurs with six taps per pair of poles, and-that with even'so low apower-"factorias 0.75, the relative hottest spot loss with twenty-tour taps is only 55 per cent. of that with six taps. It has been desirable at this pointto-introduce the .foregoing'discussion, since a number of figures to which allusion will next be made, are accompanied with the diagrammatic representation-.01 means for'obtaining various numbers of taps per ;pair of poles by various arrangements of transformer windae have already briefly described the manner in'whi'c h we obtain'twelve taps from the secondary winding of the transformer T. As heretofore explained, these twelve taps are so obtained as to constitute a twelvephase secondary winding. The primary winding of the transformer consists of a star-connected three-phase winding AB"C and a delta-connected three-phase winding D-EF. These two three-phase primary windings maybe connected as represented in Figs. 2 or 3. 'The arrangement of the primar winding represented in Fig. 2 may be pre erable to that represented in Fig. 3, since transformers operated in parallel with one another may be subject to trouble through unequal division of the load due to slight inequalities of one sort or another. The two phase-windings or coils of the secondary winding 37 inductively associated with the primaryphase-winding A are designated by reference characters a and a and the other secondary coils .are similarly designated. The secondary coils may be mesh-connected,

asreprese'nted in Fig. '2, or star-connected,

-cally illustrated -.a modified. connection .of the in Fig. 9, and it will be understoodthat the star-connectedthree-phase primary winding AB.C is. connected to the slip ringst35 inany suitable manner, .aszfor example as represented in Fig. 13 of the drawings.

jEach phase-winding orcoil of the primary winding has three secondaryswindings or coils associated therewith. Twoof the three secondary coils associated with eaolnprimary coil have thesame number (if turns, while the third secondary. .coil 'has twice as .many turns as either of, *tl1e',otl1er two secondary coils. ,In Fig. ,10 lthelegendeddinesn'epresent the vectors of .the'; co1'respondi11g coils of-the secondary winding.- Thus,.i.n Fig. 10, the vectors-25 ,11 andxii indicate the arrangement, electrical connection and relation of the .correspondingsecondary COllSfd d d and soon. The primaryphase-win 'ing D is displaced in phase 9.0 electrical degrees from the primaryphase-winding A, as will 'be evident from an inspection of Figs. 2 and 3, and,v accordingl (the :secondary coils d (Z and d will'be displaced in phase by 90 electrical degrees from the secondary coils a a and a and so on, as represented by the vectors-of Fig. 10. The larger coils a 6 etc., are connected at their middle points to form a common neutral, while the smaller coils a a 1),, I2 etc., are connected between appropriate terminals of the larger coils asdiagrammatically indicatedby the vector diagram of 10. ,The corners of the vector diagram of Fig. 10 form the twelve terminals of the resultant twelvephase secondary winding, and are connected as heretofore explained to appropriate points of the armature winding of the machine R.

In Figs. 11 and 12 we have diagrammatically illustrated a simple connectlon of the secondary winding ofthe transformer T for obtaining twenty-four tapsper pair of oles of the machine R. Here again, two t reephase primarywindings are used, but both primary windings are delta-connected, as represented in 'Fig. 11'. The delta-connected threehase primary windings DEF and D"l'-F are thus connected in parallel to the slip rings 35. 'Fig. 12 represents by vectors the arrangement of the secondary coils of the transformer. The vectors are legended to correspond to the secondary coils of Fig. 11, and it will be observed that the secondary coils (Z and (Z have fewer turns than the secondary coils (2' and (Z1 2 of the same phase of the other three-phase transformer. When the secondary coils associated with the two three-phase primary windings have the relative number of turns represented by the lengths of the vectors of Fig. 12 and are arranged as indicated by these vectors, twenty-four taps are obtained and a twenty-four phase secondary winding results in effect. These twenty-four taps are connected to appropriate points of the armature winding of the machine R.

In Figs. 13 and 15 there is diagrammatically represented'a modified arrangementfor obtaining a twenty-four phase secondary winding of the transformer T. Twentyfour taps per pair of poles are again provided as in the arrangement of Figs. 11 and 12, but each of the cords of the vector diagram of Fig. 15 is of the'fsame length. The arrangement involves the employment of a star-connection of the primary winding A-BC and a'delta-connection of the pri mary winding D--E-F. The correspond ing vector diagram of the six primary windings or coils is represented in Fig. 14, and it will be noted that the winding A is in phasequadrature with the winding D, and the windings B and C are in phase quadrature with the windings E and F, respectively. Each primary winding or coil has associated therewith two secondary windings or coils, each of the same'number of turns. These secondary coils are designated (1 ,0 5 b 01, 02 1, 2: 17 2: f1 and f2- Thus? We have twelve secondary coils and twenty-four taps, and these coils are arranged as represented by the corresponding vectors of Fig. 15, whereby a substantially twenty-four phase secondary winding is obtained. In order that each secondary coil shall give the same voltage, the relative numbers of turns or amount of magnetic flux in the star-connected primary winding A BC and in the delta-connected primary winding DE F must be appropriately chosen. Instead of having the delta-connected primary windings in parallel with the star-connected primary windings. they may, with appropriate proportions of turns, or flux, constitute a delta internal to the star-connected primary windings as hereinbefore described. Another arrangement for obtaining a twenty-four phase secondary winding, and hence twenty-four taps per pair of poles of.

' the machine R is diagrammatically represented in Figs. 16 and 17. The primary winding here again consists of two threephase primary windings, one DD-EE- FF being mesh-connected, and the other AA BB CC being star connected. Each phase winding or coil of the primary winding has six secondary coils associated therewith, of which four (a a a',, 0/ have the same number of turns, while the other two (a and a' have substantially twice as many turns as each of the other four. The manner 1n which the secondary coils are interconnected is diagrammatically represented in Fig. 17. The outer circle of coils representsthe two three-phase primary windings, but it should be noted that there need not in-reality be twelve'separate primary windings or coils, since the coils desig nated A and A in Fig. 17 may constitute the single coil AA of Fig. 16. The divided arrangement shown in Fig. 17 is more convenient for indicating the connections of the secondary coils. The larger secondary coils a a,, 6 6' 0 0' etc., have one terminal connected to a common neutral, while the other terminals of these coils constitute twelve taps of the twenty-four phase secondary winding. The intermediate twelve taps of the twenty-four phase winding are formed by connectingin series two of the smaller secondary coils differing inphase by 30 electrical degrees, where one terminal of these series-connected coils is'connected to the common neutral and the other terminal constitutes one of the twenty-four terminals of the secondary winding. The vectors of Fig. 17 are legended with the reference characters of the corresponding secondary coils, and the electrical connections and relations of the coils will be obvious to those skilled in the art from the diagram of this figure.

An arrangement of the primary and secondary windings of the transformer T for obtaining thirty-six taps per pair of poles of the machine R is diagrammatically represented in Figs. 18 'and 19. The two threephase primary windings ABC and D- EF are again starand delta-connected, respectively. Each phase-winding of the primary windings has associated therewith four secondary coils or windings, of which two have a greater number of turns than the others. These secondary coils are designated a a a a 6 6 etc., where the coils a and (1 have the same number of turns and a greater number of turns than the coils a, and a Fig. 19 represents the vectors of the secondary coils shown in Fig. 18, and illustrates the electrical connections and relations of these secondary coils. The vectors are designated by the same reference characters as the corresponding secondary coils, and the connections and arrangements of the coils will be clearly understood from the diagram of Fig. 19, in view of the preceding similar arrangements. It will be evident that thirty-six taps are thus provided, and a thirty-six phase secondary winding is obtained.

Multiplication of the secondary phases may also be obtained by so locating some of the secondary coils in their relation to the magnetic circuits that they experience in various degrees the influence of primary windings of different phases. This is in contrast to the arrangement in which two secondary coils, each exclusively under the influence of primaries of different phases, are connected in series to obtain the intermediate phase.

In Fig. 20 is shown a magnetic system with twelve windingwindows in a magnetic core 60. A single primary winding or coil is wound or threaded through each winding window. Thus, there are altogether twelve priinar coils legended A, A,

B, C, G, D, D, E, F, and F. The correspondingly legended primary coils A and A, etc., are connected in series. The series-connected coils A--A, B-B and CC are star-connected, while the seriesconnected coils D-D',' E-E, and FF are delta-connected to the three collector rings 35, as diagrammatically represented in ig. 21. The secondary coils a, a, 6, Z), '0, 0', d, d, e, c, f and f are exclusively under the influence of the correspondingly legended primary coils, whereas the secondary coils af, fb, bd, 60, 0e, ea, af, f'b, 'b'd, dc', 0'6, and ea are under the influence of the two correspondingly legended adjacent primary coils. Thus, the phase of the secondary coil of is the resultant of the phases of the two adjacent primary coils A and F. Thus, there are twenty-four secondary coils from which electricity can be supplied to the synchronous converter R through twenty-four taps per pair of poles. In Fig. 22, the vector diagram of the secondary coils of Fig. 20 diagrammatically indicates a suitable connection of these coils for obtaining twenty-four taps per pair of poles of the machine R. Diametrically opposite, that is correspondingly legended, secondary coils are connected in series with one another, since they are in the same phase, and the centers of these series-con nected coils are connected together to form a common neutral.

In Fig. 20, the secondary coil a is shown at the opposite side of the winding window from the primary coil A, but as a matter of fact thiswould rarely be the case in actual practice, since the secondary coil a would usually be located suitably close to the primary coil A to obtain the necessary minimization of reactance. Indeed, Fig. 20, is to be regarded as merely diagrammatic, and not only the primary coils but the secondary coils could well, in many instances, be suitably subdivided, intermixed and distributed. This distribution may to advantage be in slots similar to the armature slots of a direct current dynamo-electric machine. It would be superfluous to enter upon the possible mechanical space arrangements to which resort may be had in carrying out this principle, but we wish to call attention particularly to two arrangements which have been found advantageous for a multiplication of the secondary phases in accordance with the principles just outlined.

Fig. 23 is a winding diagram of the primary and secondary windings of a transformer embodying the principle of phase multiplication just described. It will be understood by those skilled in the art that the magnetic core of the transformer resembles the magnetic core of the armature of a direct current dynamo-electric machine and that the coils represented in the winding diagram of Fig. 23 are assembled in suitable slots in this magnetic core, as indicated in the diagram. In the layout of Fig. 23, only three primary slots and twelve secondary slots are employed per pole of the transformer; The transformer has a ten-pole winding and is used incombination with a twenty-pole synchronous converter winding. The figure shows the relative locations of the primary and secondary slots of the various phases. A detail view of one of the laminations of which the magnetic core is composed illustrating the relative arrangement of the primary and secondary slots is shown in Fig. 24. The corresponding part of the winding diagram connecting the secondary winding of the transformer to the armature winding of the synchrononus converter lies between M and N of Fig. 23. This portion MN if repeated five times will give the complete diagram. A considerable portion of the complete diagram is shown in Fig. 23. It willbe observed that the transformer is located on the other side of the commutator from the side occupied by the armature winding of the synchronous converter. Where this plan is adopted. the connections from the secondary terminals of the transformer are carried straight to the commutator segments. This is the arrangement" illustrated in the diagram of Fig. 23. Every fourth commutator segment is shown as indicated at the top of Fig. 23, where the commutator segments are numbered from 8 onward to 8 and again from s to 8 There are altogether 80 commutator segments and a transformer connection goes straight into each fourth segment. For the case under consideration, namely, a ten-pole transformer and a twenty-pole synchronous converter, this gives good proportions. While criticism would naturally be directed to six different V-shaped connections which are required from the secondary terminals to the commutator segments, it should be pointed out that although these six different shapes are necessary, there will be required ten of each one of these six shapes, and it should be further noted that they are of exceedingly simple construction. In all other respects the connections of the transformer windings are exceedingly simple and regular. In-designsof these'proportio'ns', there will only b'e-a' very few, say-two or three conductors: per. secondaryslot, andth'e de sign oould be planned so that these second" ary conductors could be thrust through holes from end-to end. 'Inthe arrangement-shownin Fig-"23; there are only twelve secondary phases',-;but the :principle can be developed to. provide twenty-four phases. .TllBUCOHlr' mutaton in the design ;to ;which;-Fig. -23 ap plies yhas twentyfour -lsegments per pole, and; this would also :be -a'n appropriate I numberafor' a twenty-four phase design.

- Turning toia closer consideration of. .the transformer, attentionsh'ould be directed to the. four conductor, elements, comprising conductors c ,:,c ;f, c. and 10 .5 It will be observed that theseiconductors-line up very,

closely-withthe A-coil sides ofrthe primary; Winding, 'Gonsequently this ,.elen'1entary group isl legendedf'a... -.Gon"sider next the secon clary-;. element =eonsisting of conductors 0 .50 0?? and s; i'lll'iese :li'ne'; up; with :the B-coil sides, dilduiihlSjGlGiIlGIlt of gtheyse'cond -v; any -;winding;.-is :lgnded 5.21).; 5 e-Finallyy the L Y secondary; element comprising conductors.-

03,103,20 and .c.' ;-is legended c and lines" 1.11. with the ;G-co;i :lc Isidesrof; the primary.- winding; Gnsideratibn rshould: next the gii'en to: the secondary element4consisting :of

conductors -c ,--c. ,-,c3? and 0 It :will be. observed that; I these conductors g liewequall *1 underthe influencev of. coil sides .Aand oi the primary windings and. for this "reason this'secondary element is legended ab: Siniila'r explanation could .be made for secondary elements legended 160 and ca, but theidea ought now: to beclear from the preceding description. A. a 1 4--- 1 The above; plan amounts. to obtaining six secondary phases outa-of three primary. phases and presents certain aspects'of dif-- ference. from thehplans-described in the earlier: portions, got this specification; The six secondary, phaseseach have two terminals, so that-there are twelve taps per pair of poles, The arrangement thus ivo'uld usually-.be called twelve-phase Obviously, twenty-four phases could be obtained from three phases byan extension of this principle, similarly, 8, 16, etc., phases-could be obtained from a quarter-phase supply. In

arranging for sixteen phases from a quarter phase supply it inight, bepreferred to have eight primary slots perpolIe and em ploy two sets of primary coils, the one set being connected mesh and the other set being co'nnected star;

'ljheinany advantages of the improved apparatus of our present invention will be more-clearly appreciated by considering a concrete :vex ainple. For this urposejwe havediagrammatically illustrated in Fig. 25 a winding diagram ofa 25 -cycle outfit capahie of delivering 3,500 KW at the commuta-torat: 310 volts and 11,300 amperes. The outfit is, furtherrn'or'e,icapable of giving this. same current at any commutator.:pressure downto 2&0 volts. For obtaining'thisvolt age regulation at the commutator the usual '70 plan is either to provide a synchronous booster as a component of the apparatus, or" else to provide an induction regulator. The dynamo-electric machine of-tlie outfit-hastwentypoles and is designed for operation at a speed of 150 R. PLM'; The transformer carriedon the rotatable shaft is designed to step the line pressure of 6,600 Volts dew-'11 to secondary pressures'ofs200-yolts which are-- tapped in atappropriate "places'at the end connections of the armature wvindingof the synchronous converter." Twenty-four taps per pair of poles are employed in the design illustrated in Fig. 'The slip rings are designedfor 6,600 volts, and ifI'OID. them are suppliedtwo' primary groups of coils, one: group A'B C being" star-connected and the other group being delta' con necte'd-vand the tWos-groups being connected 1 in-parallel' withione anotherx'zfiertain ad vantages, however, accrue to? the alternative plan of having these two "primary groups of coils in..'series that is,*ha ing'-the star connected coils iadiate froin the corners of the, delta-connected coils.. 5 By this latter arrangement faults are overcome which l ni l lfi be quite troublesome ivher the-star con-'-= nected and. delta-connected coilsr'ai'e con fl, nected' to ,the slip rings in parallel'.'- The design under consideration is; however,- pro-' porti'oned with the star and delta windings-3 to be in parallel The transformer hasten poles and may be-regarded as theequi alent I of five three-phase transformers, since it has? five pairs of poles. There are'sixty-priinary slots and one hundred and twenty secondary 3 slots. Thirty of-the primaryslotslbelong.v

to the star-connected coils while the other thii-ty slots belong to the delta conne'cted 001 s. star-connected coils has twenty-eight 'c0n'-. ductors arranged one Wide and twenty-eight deep, while each of the primary. slots be-p longing to the delta-connected coils contains forty-eight conductors. Each secondary slot contains eight conductors arranged four Wide and two deep. Each secondarycon' due-tor carries 290 ampere's." In the starconnected primary circuits, eacli'primary conductor carries 160 amperes; Attention is called to the small amount'of current per secondary conductor. The high ainount of sub-division of the secondary Winding intomany parallel circuits is among theinany important advantages secured by our iii-.125 vent-ion. The prin'iaryPR loss is 17,000 watts; The secondary 1 R- loss is 23,000 Watts. The total copper loss is 40,00O wattsx The total iron lossis 36,000 Watts. The total of all losses is 70,000 Watts, exclusive Each primary s'lot devoted to the 110 an efliciency at rated load of ninety-eight per cent. The total Weight of copper in the transformer is some 6,000 to 7,000 pounds and the total weight of sheet iron is some 40,000 to 50,000 pounds. This should be compared with stationary transformers which have heretofore been furnished in connection with 3,500 KW synchronous converters. In such stationary transformers, the copper weighs about. 7,660 pounds and the sheet iron about 27,000 pounds- In accordance with our present invention, how-. ever, the outlays for tanks, oil, water, circulation, coils and various other auxiliary features of stationary transformers are eliminated. It should furthermore be remembered that by our invention, the six large collector rings heretofore used onsynchronous converters are displaced by threerelatively small collector rings. Furthermore, the improvements effected by employing twenty-four phases cheapen the synchronous converter of the outfit and improve the' converter itself in several respects, notably in the matters of commutatlon and uniform temperature distribution.

skilled in the art in view of the foregoing explanation. The lower portion of the diagram relates to the six-phase primary wind ing carried in the sixty slots of the trans former core. The phase-windings or coils ofthe primary winding are designated A, B, C, D, E, and F, just as in the preceding examples of phase multiplication. The diagram 'of the secondary winding is shown 1 just above the diagram of the primary winding. The portion of the diagram between the points designated M and N is repeated five times in making up the complete winding diagram. The conductors of the secondary winding of the transformer are legended to indicate the phase-winding of the primary winding under whose influence they lie. Thus, the secondary conductors designated a come under the influence of the primary phase-winding A, and the secondary conductors ad come under the influence of the primary phase-windings A and D, and so on. Above the diagram of the secondary winding of the transformer are shown the connections whereby the secondary terminals are connected to the appropriate parts slots of the transformer core will be understood by reference to Fig. 26 which shows a portion of one of the punchings of the cores -Theimproved electricity transforming and converting apparatus of our present invention is particularly intended to replace the stationary transformers and synchronous rotary converters, and similar apparatus, heretofore used in substations and elseing current electricity and delivering low pressure direct'current electricity. The apparatus has its particular field of usefulness inlarge and densely settled communities. For such work there has been a rapid increase in the size of synchronous converters. For explanatory urposes we may take the case of a13,500 I 1 synchronous converter, having 26 polesy-and' 'ving 25 c cles with a speed of 115 R- P. 18 3,500 K V is delivered fromfth e commutator at pressures ranging from 240to 300 volts. Alternating-current. electricity is supplied to the primary winding of the transformer at 6,600 volts. W'iththetype of synchronous converter at present-customary,- there are six very large collector rings, each of which Thewinding diagram-of Fig. 25 will it is believed be readily understood by thosewith its equi pment ofibrush es has to be designed to transmit about 5,000 amperes. In our apparatus, these six enormous collector rings are replaced by three relatively small collector-rings, which with their equipment of brushes will each have the duty of trans mitting. only about'300 amperes; Of course these three small collector rings have to be designed and insulated for 6,600 volts, as against the relatively low voltage of the collector rings in the present day outfit. There thus becomes available practically all the space now occupied by the six large collector rings In ourimproved apparatus, the rotatable transformer can be mounted on the shaft of the synchronous converter in a space not much larger than that now occupied by the six large collector rings.

-Ou1' improved arrangement, howeven' where for receiving high pressure alternat as against the six taps per pair of poles now usually employed. Indeed, there is no particular limit to the number of taps per pair of poles which can be readily used when the transformer and armature windings rotate as a unit, and where any noteworthy economy is obtainable in going beyond twelve tapsper pair of poles, it can be conveniently done, as hereinbefore described, whereas in the case of the present day synchronous converter outfit, an increase of the number of collector rin s has been considered by those skilled in the art as involving magnetic arrangements, in going from six to 1 33'? ioc we's'hort ci'rcuit all this delay, and obtainthe advantages of twelve or more collector rings without theattendant disadvantages which htive heretofore prevented the adoption of morethan six taps per pair of poles.

of the rot ry converter.

It is well here to dwell a little more at length on the advantages of twelve collector rings, since the older theoretical disquisitions were to the effect that nearly all the possible advantage was obtained in going fro'mth'ree to six collector rings, and that the further advantages, as regards electrotWlV rings W'Ould'dnly be of the 'OrderOf 10 per cent, or thereabout. Fo'rmerly those skilled in the art were not sufficiently conversant with the facts" relating to the differeiice in heating'at different parts of the armature coils' The greatest heating is at thetap coils and the intermediate coils are very much less heated. The ratio of the heating in the hottest coils to the heating in the coolest coils is very high in a machine with three taps per pair of poles. It is mueh'lo'wer in a machine with six taps per pair of poles, and it is till'lowe in a ma chine with t"welve taps per pair of poles. Furthermore, as weincrease the number of taps per pair ofpoles we are able, by means of resortto a fractional pitch winding where the fractional pitch is not much less than the full pitch, to distribute the tap coils more uniformly among the slots. For example, where we have twelve taps per pair of poles we can, inlighting rotaries, with a winding pitch of about 95 per cent, have in every slot a pair of coil sides, one of which is atap coil and consequently would ordinarily run at a high temperature and the other of which is a coil one-half way between taps and would ordinarily run at a low temperature. By simple expedients in the thermal design we can arrange for the two coils and the magnetic core to so share one anothers heat energy that the difference between the temperatures in the two coils will be relatively small as compared with present practice. It is obvious that the temperature of the tap coils limits the rating of the machine, and in view of the foregoing explanation it will be clear that the increase in rating, due to the use of an increased number of taps per pair of poles, is greater than would be deduced from the consideration of the total armature PR losses. Furthermore, the more taps per pair of poles, the greater is the percentage of the total input to the synchronous converter which passes directly through the armature to the commutator without involving any inefficient energy transformation. Consequently, a gradual increase in efficiency is attained by an increase in the number of taps per pair of poles. Furthermore, with such an increase in the number of taps per pair of poles what may be called the local-symmetry is greater threughout the design. lVith three taps per pair of poles we can have a perfectly symmetrical design, when considering the design as a whole, but we do not have the quality for which'the term .local symmetry has been employed above.

This is obtained throughout the periphery of'the armature to a much greater'degree by employing many taps per pair of poles- This improvement in the local symmetry will beassociated "with material improvement in commutation.' The heating of a commutator is by no means due exclusively to the friction and legitimate PR losses 'at the brush contacts, but is in considerable measure due also to the useless currents flowing during the period of coiiiiiiutatibn of each coil. \Ve arrive much furtlie1"'to'-, ward the ideal of utterly eliminating these commutation losses, which are not confined to the commutator but occur in all parts of the coil undergoing commutation as well as in the neighboring parts of the coil, when we use a large number of-taps per pair of poles. By taking intelligent advantage of all these gains, we are. able, by the application of our present invention, to either improve the quality of a synchronous converter for a given output, or else for a givenquality to appreciablydecrease the size and cost of the converter.

Two further advantages may in addition be obtained as a result of the improvement in the commutation due to the use 'of an increased number of taps per pair of poles. In certain cases the improvement in the commutation is such that the interpole's, heretofore generally employed, may satisfactorily be dispensed with. This permits of slightly decreasing the pole pitch, which works in nicely with the decreased size of armature conductors, which becomes pos sible when the number of taps per pair of poles is increased. Then too, the improvement in the commutation enables us to operate the rotary at higher speeds than has heretofore been considered "practicable;

The design of the transformer in our improved apparatus adapts itself admirably to obtaining high reactance. Indeed, the design in actual practice has as high reactance as is desired for regulation of the commutator voltage by field control. This is in lot.

striking contrast with the present day outfits, where in some cases, central stations LC'- tually pay more for transformers with high; reactance, although the. transformers in -q1iestionhave undesirable characteristics as regards stray losses and efficiency. Another advantage of our improved apparatus which windingof. the transformer canbe divided into ,a ,largenumb er of independent circuits, thus decreasing the amount of. current flowing' in-any secondary winding circuit. For. lowyoltage. synchronous converters of veryar a jtp t-it ma t d a e are. a ay. fib a-1 1. i' ery sxre s e ll erya t whichhaye, been" customary; iii-the secondary windin i u ts a d. t em oy n ead: manysecpndarycircuits, each of a ,few. turns; 1 of .wiregof fairly. small. crosssection. I Since in...our.irnproved. apparatus the secondary din qe u rsps ti e the. transformer to the synchronous converter,

the seeofidarynvinding can bedivided into (zip) independent secondary circuits, .eachproportion? for; a; relatively small current,

where t .is the number. of tapsper pair of polesand ,p; is the number of pairs of poles of theconverten, Inthis manner we at once overcome one of the very reat est obj ectionable {features cf .the or ary ;station ary transformenf0r synchronous converters, namely, the heavy, unwieldy, and expensive secondary windings.

In all of the embodiments of our invention hereinbefore described, the primaryand secondary windings of the transformer have rotated as a unit. Theinvention may, howeyer, be very advantageously carried out by rotating only the secondary windlng of the transformer and assembling the primarywindingon a stationary core, section as described and claimed in the-copending.

application of Henry M. Hobart, Ser. No. 121,504, filed September 21, 1916. Certain of the appended claims, therefore, cover this modification of the invention as well as those particularly described herein.

lVe have herein shown andparticularlydescribed certainembodiments of our invention for the purpose of explainingits principle and showing its applications, but numerous modifications in the details of construction and arrangements of these embodiments and other applications will pre- 1'. electricity, transforming and ,converting apparatus comprising a synchronous conyerten having a magnetic field system and an armatureuwinding adapted rotate.

her n, a dla @r ase '-mu yi t a -r former having a primary winding. connected.

5 p rings-amL-as wn a y w g c n nected to said armature winding, said arma ture and transformenwindings and saidslip. rings being carried; by the rotatable element of said apparatus 2. An; electrici, y transforming con verbilig ppa a us .QQ PElS g a sy chr n converter having. a, rotatable shaft, a mag-, netic core mgnnted. on g saidshaft, an ,ar ma i ture, winding carried by said core, slip; rings eu t dn i ehafiil ni a. Pha ifi i: p i ene or r ea r edlby sai s t and 1 having. primary and. secondary, .windings electrically. connected between said slip rings and a a inat re-W di 3+ An electricity atransforming and con-' verting apparatus comprising a Irotatable shaft, slip ringsmounted, on said shaft, synchronous converter having. a stationarv magnetic field system. and an armature, wind; j ingearried, by said shaft, and, a pliasemultiplying transformer carried by. said' shaft, and having primary and secondary .windings. one. of which windingsiis connected; to said slip rings while the other winding is connected to said. fmature winding.

4. An electricity transforming-and -con' verting apparatus comprising a synchronous converter having a stationary magnetic field system. and 'a rotatable. member.- carrying an armature winding; so,- thatthe armature windin is adapted torotate within said magnetlc' fieldsystem, slip rings carried by said rotatable member,.;and a transformer having primary and secondary windings carried by-said rotatable member, the pri-- mary winding of saidtransformer being arranged gas a. six phase winding electrically connected tosaidslip rings, the secondarywinding of said transformer being arranged to produceagreater number. of phases than the primary winding and having its terininals electrically connected to appropriate points of said armature winding.

:5. An electricity transforming and 'converting "apparatus comprising a rotatable member, a stationary magnetic field system, an armature winding carried by said rotatablejnember and associated with said magnetic field system to form a synchronous converter, a transformer havingprimary 4 and secondary windings carried by said ro- 

